Method and apparatus for analyzing flue gas



em; 12,, 19% s. CHASE 2,533,436

METHOD AND APPARATUS FOR ANALYZING FLUE GAS Filed Jan. 13, 1945 3 Sheets-Sheet l INVENTOR.

E s A H Q s METHOD AND APPARATUS FOR ANALYZING FLUE GAS 3 Sheets-Sheet 2 Filed Jan. 15, 1945 w I l u QNN WNN INVENTOR.

Dec, 12,, 1950 s, QHASE 2,533,436L? METHOD AND APPARATUS FOR ANALYZING FLUE GAS Filed Jan. 15, 1945 3 Sheets-Sheet 3 Patented Dec. 12, 1959 METHOD AND APPARATUS FOR ANALYZING FLUE GAS Sherman Chase, Evergreen Park, 111., assignor to Carnegie-Illinois Steel Corporation, a corporation of New Jersey Application January 13, 1945, Serial No. 572,715

8' Claims.

This invention relates to a method and apparatus for combustion control by usin fractional or incremental combustion principles in cascade. Liquid, solid and gaseous fuels, whichare used in combustion. chambers and the like, vary in quality and quantity, thus requiring continuous adjustment of the rate at which air is supplied. In some cases more than one fuel is burned, thisrequiring a multiplicity of summarizing devices. Various types of controls are in use at present, but they are all relatively complicated and expensive. In some cases, particularly when the air requirements are relatively constant, the line gas is analyzed in order. to determine whether'or not the correct amount of air is being suppliedto the burner and the air supply is then controlled manually. The apparatus used to analyze the flue gas is also relatively complicated and'expensive.

It is an object of my invention to provide'a method and apparatus for controlling the ratio of air to fuels within practical limits of economy and desirability in order to obtain in a simple manner substantially perfect combustion.

Another object of my invention is to provide simple means for analyzing flue gas.

These and other objects will be more apparent after referring to the following specificationan'd attached drawings, in which:

Figure'l is a schematic diagram showing'ione embodiment of my invention;

Figure'Z is a schematic diagram showingra second embodiment of my invention; and

' Figure 3 is a schematic diagram showing a third embodiment of my invention.

Referring more particularly to Figure loithe drawings, reference numeralg indicates a' stack or other sourc of'fiue gas from which a suitable sample of the gas is drawn through a conduit '4 by a gas pump E mounted on a shaft 8. The flue gases will enterthe pump at approximately room temperature and while this temperature will'vary slightly, the rate of change will beslow so "that comparable results are obtained. A pulley it is fastened to the shaft 8 and is driven by means of a belt I2 which passes around a pulley M mounted on the shaitof a motor is. The flowfof gas will be at a constant rate since no means is provided for varying the speed of motor" it. Aconstant increment of hydrogen is added to the flue gas in the conduit lirom an electrolytic cell; it and the pump 6 delivers the mixture of flu gas and hydrogen through a pipe 2% to a conduit 22. Within the conduit are three platinum "resistors 2 l; Eli and???) through which currentipasses Y from a source of current 33. The resistors 24% and 25 each form one leg of aWheatstone bridge, the other legs being resistors 3-2 and 3s. A galvanometer 3G in the Wheatstone bridge may be calibrated to indicate'the amount of excess air or the amount of carbon monoxide. Between the resistors-2 3 and 26 is aninlet '38 through which oxygen is admitted from the electrolytic cells id and 42. Power is delivered to the electrolytic cells l8, ac and 42 through the lines 44. Between the resistors 26 and '28 is an inlet do through which hydrogen is introduced from the electrolytic'cellsll and 42, the volume of hydrogen being twice that of the oxygen. From the conduit 22'the mixture of gases passes through a cooler 48 toia gas pump 50 mounted on the shaft 8 and which has the same volume characteristics as pump 6 so that for each rotation of shaft 8,'the volume of gas pumped by either pump is equal. A'suitable type of pump for this purpose is one constructed according'to the principles of a wet typegas meter,-which, when rotated by a source ofpower, is capable of acting as a gas pump. A pipe 52 leads from the suction end of pump 5 to a diaphragm chamber 54 whose diaphragm transmits the pressure from the suction side of pump 6 to a beam 56 which is suitably pivoted at'EB. A pipe 'Sll leads from the suction end of pump 59 to a diaphragm chamber 62, whose diaphragm transmits pressurefrom the suction side of pump to the beamlifito oppose the pressure exerted by the'diaphragm in chamber 55. The beam 58 is suitably counterbalanced by spring 6 and counterweight 55. The pressure of spring so may be adjusted bymeans of a screw 5% which is threaded through a suitable support it. On its free end the beam 56 carries an electrical contact l2 having a wire M connected thereto and which is movable with the beam 56 to contact one of the electrical contacts i5 and 88 to deliver current to the motor armature 88. Current is supplied to the armature so and field 52 from the power lines 83 through the switch 84. The armature shaft of the motor carries a pinion 85 which meshes with a gear 85 mounted on a, shaft '83. A lever is also mounted on the shaft 88 and through linkageSZ and changes the position of valve 96 in the air line 88.

The operation of the device is as follows:

The pump 6 delivers the mixture of flue gas and hydrogen to the conduit 22. If there is free oxygen in the flue gas, it combines with the hydrogen in themixture to form water vapor as it passes over'the heated resistor zfi, thus reducing the volume of the mixture anamount equal to three times the volume of the oxygen. The burning of the hydrogen and oxygen develops heat which changes the resistance of resistor 2 to unbalance the Wheatstone bridge and the galvanometer 35 will indicate the amount of excess air. The oxygen entering'at 33 and the hydrogen entering at 45 will combine to form water vapor and will have no eifect on the volume of the sample. The flue gas from the conduit 22 passes through the cooler 33 in order to bring'its temperature down to that of the flue gas drawn into pump 6 and passes into the pump 58. Since the gas entering the pump 58 has a smaller volume than that entering the pump 6, the pressure on the diaphragm 52 will be less than that on diaphragm Fa l, thus completing a circuit through contactors 2 and 8 to motor 88 which operates to close air valve as to decrease the amount of air supplied to the combustion chamber.

If, instead of an excess of oxygen, the flue gas contains a combustible such as carbon monoxide, the carbon monoxide will combine with the oxygen added at 33 as it passes over the heated resistor 26 without any reduction in the volume of the flue gas. The remaining oxygen combines with hydrogen and there will be an increase in volume equal to the amount of carbon monoxide since for each volume of carbon monoxide burned there will remain one volume of hydrogen lacking oxygen for combustion. This increase in volume causes the pressure to build up at 69 so that the pressure on diaphragm 62 is greater than that on diaphragm 54, this completing a circuit through contactors l2 and M5 to motor 80 which rotates in the direction opposite to that above to cause the valve 95 to open to increase the supply of air to the combustion chamber. The burning of the combustibles at resistor 25 changes the resistance of the resistor, this unbalancing the Wheatstone bridge and the galvanometer 35 will indicate the amount of carbon monoxide.

The analyses of any commercial fuel is such that when it burns, suflicient H2O is formed so that the flue gas when cooled to room or atmospherictemperature will be saturated with water vapor. Furthermore, since the gas sample passes through the wet type gas pump 3 it necessarily becomes saturated. Since the cooler e8 reduces the temperature of the gas to room temperature, the H20 will not be in the form of steam and the decrease in volume will be that set forth above, since the H20 will not be in the form of gas and its volume will be negligible. Whether carbon monoxide or oxygen is present in the flue gas determines whether the volume of the sample going through the combustion tube will increase or decrease. If excess oxygen is present, the volume will decrease as set forth above and if carbon monoxide is present, the volume will increase since the hydrogen added at 16 Will'not all burn or combine.

Figure 2 shows a second embodiment of my invention which diflers from that of Figure l in the means employed for utilizin the results of the incremental combustion of the flue gas to control the air flow. The pumps 5 and 56 are omitted and the apparatus described hereinafter substituted thereioin. A conduit 99 is used in place of conduit 22 and is similar thereto in that it contains resistors 2t, 2t and 23 and associ ated Wheatstone bridge and also has the same apparatus for adding oxygen and hydrogen. I-ly-.

drogen is added from the electrolytic cell it into the conduit 99 through nipple 66.. Between nipple 100 and resistorz is an orifice plate [92 and at the other end of conduit 99 is a second orifice plate [M having an orifice about twice the area of that of orifice plate H32. There is a by-pass H36 around the orifice plates I532 and Hi l having a fluid chamber Hi8 therein. A siphon iii draws a sample into conduit 99 and if more than the desired amount of flue gas is drawn, it will bypass around the oriiice plates Hi2 and its and bubble through the water in the chamber Hit A pressure line H2 is located in the conduit on the entry side of orifice 59d and leads to a diaphragm Ht which transmits the pressure to a beam H6 which is pivotally mounted at 1 8. The beam H6 is counterbalanced by means of counterweight E22 and spring [26 which may be adjusted by means of screw i213 threaded through a suitable support H5. The beam 56 carries the contactor 72 which is adapted to contact contactor F5 or 78 of the motor circuit according to the pressure in the line 1 l2.

The operation of the device is as follows:

The differential across an orifice is proportional to the product of volume and total weight of the gases flowing therethrough and if there is an ex cess of oxygen in the flue gas the volume of the flue gas contracts causing a decrease in differential across orifice its, this completing a circuit through contactors l2 and 5'5 to motor which operates to close air valve to decrease the supply of air. If carbon monoxide or other combustibles are in the flue gas instead of free oxygen, the volume of the gas going through orifice we increases, this increasing the diiierential across the orifice and completing a circuit through contactors l2 and 18 to motor 86 causing it to rotate in the reverse direction to open air valve 96. galvanometer to indicate the amount of oxygen or combustible in the flue gas in the manner described above.

In the embodiment shown in Figure 3, the heat generated by the combustion of the gases is used to control the flow of air in addition to indicating whether or not there is excess oxygen in the flue gas. A sample of flue gas is drawn from the stack 2 by means of a pump I23 and delivered through a pipe 35.! to a conduit I 32. 53b is provided with an outlet I34 for getting rid of excess flue gas. Within the conduit 832 are two platinum resistors I35 and 38, each of which forms one leg of a Wheatstone bridge, the other legs being resis ors his and 5 32. Power is supplied to the resistors through lines use and a potentiometer controller M5 is provided in the Wheatstone bridge and is connected to control the circuit of air valve motor as in the usual manner. Hydrogen is supplied to the conduit E32 through an inlet MS from an electrolytic cell lBiJ. Between the resistors we and 38 is an inlet I52 through which oxygen is supplied to conduit I32 from electrolytic cells l5i! and :56. Power is delivered to the electrolytic cells i553 and 554 through the lines I56.

The operation of the device is as follows:

If there is free oxygen in the flue gas, it combines with the added hydrogen to form water vapor as it passes over the heated resistor I8 3. The burning of the hydrogen and oxygen develops heat which changes the resistance of resistor I36 to unbalance the Wheatstone bridge and the potentiometer controller 1% then operates to complete a circuit through contactors l2 and E8 to motor til which operates to close the air valve 96 to decrease the amount of air supe plied to the combustion chamber. Ir", instead of r The Wheatstone bridge is provided with a- The pipe 7 v an excess of oxygen, the flue gas contains a combustible such as carbon monoxide, the carbon monoxide will combine with the oxygen added at I52 as it passes over the heated resistor 938-. The burning of the carbon monoxide develops heat which changes the resistance of resistor I 38 to unbalance the Wheatstone bridge and the potentiometer controller I48 then operates to complete a circuit through contactors 12 and E6 to motor 80- Which operates in the reverse direction to open the air valve 96. to increase the amount of air supplied to the combustion chamber. It will beunderstood that the potentiometer controller I46 may be replaced by a galvanometer which iscalibrated to -indicate the amount of. excess air or the amount of carbon monoxide in the flue gas and this indication will be utilized by the operator tocontrol the flow of air to the combustion chamber.

While several embodiments of my invention have been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

I claim:

1. The method of analyzing flue gas for the presence of free oxygen or a combustible therein which comprises sampling the flue gas at a constant temperature and at a constant flow rate, adding hydrogen to the flue gas sample at a constant flow rate, passing the resultant gas mixture at a constant flow rate to an analyzing zone, burning the hydrogen with any free oxygen in the flue gas in said zone, adding oxygen to the residual flue gas sample at a constant flow rate, burning any combustible in the residual sample with the added oxygen in said zone, and determining whether the original flue gas sample contains free oxygen or a combustible in response to the heat developed by the combustion'of the gas.

2. The method of analyzing flue gas for the presence of free oxygen or a combustible therein which comprises sampling the flue gas at a constant temperature and at a constantflow rate, adding hydrogen to the flue gas sample at a constant flow rate, passing the resultant gas mixture at a constant flow rate to an analyzing zone, burning the hydrogen with any free oxygen in the flue gas on a first resistance heater in said zone, adding oxygen to the residual flue gas sample at a constant flow rate, burning any combustible in the residual sample with the added oxygen on a second resistance heater in said zone, measuring the change in resistance of the first and second resistance heaters in said analyzing zone to determin the presence of free oxygen or a combustible in the original flue gas sample.

3. The method of analyzing flue gas for the presence of free oxygen or a combustible therein which comprises sampling the flue gas at a constant temperature and at a constant flow rate, adding hydrogen to the flue gas sample at a constant flow rate, passing the resultant gas mixture at a constant flow rate to an analyzing zone, burning the hydrogen with any free oxygen in the flue gas on a first resistance heater in said zone, adding oxygen to the residual flue gas sample at a constant flow rate, burning any combustible in the residual sample with the added oxygen on a second resistance heater in said zone, adding hydrogen to the remaining flue gas sample at a constant flow rate the volume of the added hydrogen being twice that of the previously added oxygen, burning the hydrogen with any free oxygen present in the flue gas mixture on a third resistance heater in said zone, condensing any water formed during the steps of burning hydrogen, and measuring the volume of the flue gas sample prior to passing said sample to the analyzing zone and subsequently to its exit therefrom to determine the presence of free oxygen or a combustible in the original flue gas sample.

4. The method of analyzing flu gas for the presence of free oxygen or a combustible therein which comprises sampling the flue gas at a constant temperature and a constant flow rate, add ing hydrogen to the flue gas sample at a constant flow rate, passing the resultant gas mixture at a constant flow rate to an analyzing zone, burning the hydrogen with any free oxygen in the flue gas on a first resistance heater in said zone, adding oxygen to the residual flue gas sample at a constant flow rate, burning any combustible in the residual sample with the added oxygen on a second resistance heater in said zone, adding hydrogen to the remaining flue gas sample at a constant flow rate the volume of the added hydrogen being twice that of the previously added oxygen, burning the hydrogen with any free oxygen present in the flue gas mixture on a third resistance heater in said zone, condensing any water formed during the steps of burning hydrogen, determining the amount of free oxygen or a combustible present in the original flue gas sample.

5. The method of analyzing flue gas for the presence of free oxygen or a combustible therein which comprises sampling the flue gas at a constant temperature and a constant flow rate, adding hydrogen to the flue gas sample at a constant flow rate, passing the resultant gas mixture at a contact flow rate to an analyzing zone, burning the hydrogen with any free oxygen in the flue gas on a first resistance heater in said zone, adding oxygen. to the residual flue gas sample at a constant flow rate, burning any combustible in the residual sample with the added oxygen on a second resistance heater in zone, adding hydrogen to the remaining flue gas sample at a constant flow rate the volume of the added hydrogen being twice that of the previously added oxygen, burning the hydrogen with any free oxygen present in the flue gas mixture on a third resistance heater in said zone. condensing any water formed during the steps of burning hydrogen, measuring the change in resistance of the first and second resistance heaters in said analyzing zone to determine the presence of free oxygen or a combustible in the original flue gas sample.

6. Apparatus for analyzing flue gas which comprises a flue gas sampling means, a first source of hydrogen, a first conduit connecting said source to said flue gas sampling means, a second conduit which comp ises plurality of combustion zones connected to said sampling means, a first and second resistance heater located in said second conduit, a source of oxygen, a third conduit conrec" 2: said source of oxygen to said second conduit at a point between said first and second hea ers, and means responsive to the change in resistance oi the first and second resistance heaters for detecting the presence of oxygen or a combustible in the flue gas.

'7. Apparatus for analyzin flue gas which comprises a flue gas sampling means, first source of hydrogen, a first conduit connecting said source to said flue gas sampling means, a second conduit which comprises a plurality of combustion zones connected to said sampling means, a first, second and third resistance heater located in said second conduit, a source of oxygen, a third conduit connecting said source of oxygen to said second conduit at a point between said first and second heaters, a second source of hydrogen, a fourth conduit connecting said second source of hydrogen to said second conduit at a point between said second and third heaters, and means responsive to the changes in the gas due to the combustion in the second conduit for detecting the presence of oxygen or a combustible in the flue gas.

8. Apparatus for analyzing flue gas which comprises a flue gas sampiing means, a first source of hydrogen, a first conduit connecting said source to said flue gas sampling means, a second conduit which comp-rises a plurality of cornbustion zones connected to said sampling means, a first, second and third resistance heater 1ooated in said second conduit, 3, source of oxygen, a third conduit connecting said source of oxygen to said second conduit at a point between said' first and second heaters, a second source of hy- SHERMAN CHASE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,321,064 Lamb et a1. Nov. 4, 1919 1,644,123 Griswold Oct. 4,1927 1,682,689 Smoot Aug. 28, 1928 1,770,059 Barber July 8, 1930 2,005,036 Howe June 18, 1935 2,083,521 Miller June 8, 1937 2,139,902 Malmgren Dec. 13, 1938 2,229,884 Chalkey Jan. 28, 1941 

1. THE METHOD OF ANALYZING FLUE GAS FOR THE PRESENCE OF FREE OXYGEN OR A COMBUSTIBLER THEREIN WHICH COMPRISES SAMPLING THE FLUE GAS AT A CON-S STANT TEMPERATURE AND A CONSTANT FLOW RATE, ADDING HYDROGEN TO THE FLUE GAS SAMPLE AT A CONSTANT FLOW RATE, PASSING THE RESULTANT GAS MIXTURE AT A CONSTANT FLOW RATE TO AN ANALYZING ZONE, BURNING THE HYDROGEN WITH ANY FREE OXYGEN IN THE FLUE GAS IN SAID ZONE, ADDING OXYGEN TO THE RESIDUAL FLUE GAS SAMPLE AT A CONSTANT FLOW RATE, BURNIGN ANY COMBUSTIBLE IN TEH RESIDUAL SAMPLE WITH THE ADDED OXYGEN IN SAID ZONE, AND DETERMINING WHETHER THE ORIGINAL FLUE GAS SAMPLE CONTAINS FREE OXYUGEN OR A COMBUSTIBLE IN RESPONSE TO THE HEAT DEVELOPED BY THE COMBUSION OF THE GAS. 